Herpes simplex virus (HSV) and Varicella-Zoster virus (VZV) are alphaherpesviruses that cause oral/genital herpes and chickenpox/zoster respectvely. They are enveloped viruses with relatively large genomes with the coding capacity for more than 70 unique genes. The expression of genes in alphaherpesviruses are temporally regulated and three putative each kinetic classes have been defined: immediate early, early and late genes. The immediate early genes encode proteins that regulate the expression of genes of other kinetic classes thus playing a pivotal role in the life cycle of the herpesviruses. These alphaherpes viral immediate early proteins not only provide excellent model systems to study eukaryotic gene regulation in general but also understanding the regulatory mechanics of these proteins provide protential molecular targets that could be exploited for therapeutic interventions. Current efforts focus on four HSV regulatory proteins: ICPO, ICP4, ICP27 and VP16. Our recent studies indicate that the ICP27 is a RNA-binding protein that stabliszes unstable mRNA by specifically interacting with the 3' RNA-processing signals of a particular transcript. In addition, the ability of this protein to interact with the basal transcription factors TFIIB and TBP has been demonstrated. To identify the cellular proteins that interact with these HSV regulatory proteins to mediate their transcriptional effects, we have made use of the "Yeast two-hybrid" system and are currently screening a cellular cDNA library derived from HeLa cells. The three VZV transregulatory proteins under investigation are IE62, ORF4 and ORF10. Our recent studies have illustrated that the IE62 -dependent activation of responsive promoters are mediated by a unique mechanism involving the TATA element of the promoter. Studies are in progress to delineate the interactions of IE62 with the transcriptional machinery of the Pol ll promoters and the preliminary evidence indicate that IE62 not only interacts with the basal transcription factors TfllB and TBP but also interacts with the cellular transcription factor USF. Using saturation and site specific mutagenesis, further dissection of the functional domains of IE62 are being pursued.